This field is activated only if you have configured the setting Manage Invoicing Plans on Quotes/Customer Orders under Invoicing plans under the Sales tab in the Settings procedure.
Here you can select an invoicing plan for a quote. These invoicing plans must be registered in the Invoicing / Payment Plans procedure in the Global Settings. If you select an invoicing plan, the Invoicing plan tab opens where you can adjust the invoicing plan if needed. If you leave this field empty, the invoicing of a future customer order will be made as usual.
You can also change invoicing plan on an existing quote with a selected invoicing plan (as long as the quote status is not 8-9). A warning then appears saying that the old invoicing plan will be deleted.
If you have selected an invoicing plan for the quote it will remain when the quote is converted into a customer order. However, any changes made afterwards in the invoicing plan on the customer order will not affect the quote. You can also delete and add invoicing plans directly on the customer order.